This invention relates to a device for indicating the charge status of a battery during charging and/or discharging, comprising:
a power-supply circuit for charging the battery and/or energizing a load;
means for generating pulses during charging and/or discharging of the battery;
computing means for computing the charge status on the basis of the generated pulses, and
indicator means for indicating the computed charge status.
Such a device is suitable for use in rechargeable apparatuses, in particular in rechargeable electronic showers.
Such a device is known from German patent application No. 2,313,566. During charging and discharging of the battery this device measures the charging and discharging currents by means of a resistor connected in series with the battery. The voltage across this resistor is amplified and then integrated, the gain and the integration constant during discharging being different from those during charging of the battery. The integrated voltage is compared with a reference voltage and each time that this reference voltage is reached a pulse is generated. These pulses are supplied to a counter whose count is displayed by means of an indicator which indicates the charge status of the battery. When the battery is discharged a warning signal is generated as soon as a specific count is reached and after a certain time the load is disconnected from the battery to preclude complete discharging of the battery. During charging of the battery the charging circuit is disconnected when a maximum count is reached to prevent the battery from becoming overcharged.
A disadvantage of this known device is that for determining the charge status it is necessary to connect a resistor in series with the load between the battery terminals. As a result of this the known device is not suitable for use in, for example, a rechargeable electronic shaver, in which the load is constituted by a motor. When this motor is energized by the battery, the voltage drop across the resistor should be very small, because otherwise the motor characteristic will be affected adversely. To avoid this adverse effect the resistor should be of such a low value that handling the voltage across this resistor presents major problems. Moreover, the known device does not allow for deviations from the nominal capacity of the battery, for example as a result of ageing.